The first disclosure of polysiloxane polyoxyalkylene copolymers appears in U.S. Pat. No. 2,834,748. These compositions were of the hydrolyzable type. Subsequently, the first disclosure of non-hydrolyzable polysiloxane polyoxyalkylene copolymers appeared in U.S. Pat. No. 2,846,458. In 1958 the first application of polysiloxane polyoxyalkylene copolymers for the stabilization of urethane foam appeared in British Patent 892,136. These polymers were of the hydrolyzable type. The application of nonhydrolyzable copolymers to the production of urethane foams followed shortly thereafter.
To those skilled in the art, it is known that the purity of non-hydrolyzable silicone polyether compositions used in the stabilization of urethane foams typically suffers due, in part, to the requirement that molar excesses of process polyethers be used to ensure complete consumption of silanic hydrogen from the siloxane intermediate. This requirement arises due to competing side reactions of the olefinically terminated polyether which effectively inactivates a certain proportion of the polyether. Residual silanic hydrogen remaining in the product, as is well known to those skilled in the art, can lead to product inconsistencies and/or defoaming properties in the product when used in urethane foam systems. The use of excess process polyether not only leads to an effectively diluted product, but also increases the cost of manufacture and inhibits facile isolation of copolymeric product (if and when desired).
Unreacted silicones (particularly non-modified cyclics) which are present as part of the thermodynamic equilibrium of species present in an equilibrated poly(dimethyl-methyl hydrogen) siloxane fluid also reduce the purity of the copolymeric products prepared therefrom.
Additionally, the compositions of typical copolymers, as described above, necessarily show a broad molecular weight and compositional distribution, which are partially a function of the nature of the equilibrated siloxane intermediates used. Hence, an application which may effectively require a specific narrow copolymer molecular weight and/or compositional distribution for performance efficacy could be complicated by the presence of a broad distribution. At the very least, the copolymeric structures falling outside the specific narrow molecular weight and/or compositional distribution would serve as an expensive diluent to the specific product and process.
The issue of excess polyether has been addresses in several U.S. Pat. Nos. such as, 3,798,253; 3,957,843; 4,059,605; 4,150,048; 4,160,775 and the like. These patents all follow the common theme of modifying the functional portion of the process polyether so as to minimize the mechanism by which a substantial portion of the polyether is inactivated with regard to its hydrosilation reactivity. This method does allow for a somewhat more pure copolymer devoid of substantial unreacted polyether diluent. Unfortunately, the reactivity of the modified process polyethers in those examples is considerably diminished relative to the unmodified analogs. Additionally, these methods do not address the issue of the broad molecular distribution of the copolymeric species, nor the presence of non-modified silicone species.
The issue of molecular weight and compositional distribution has been discussed in U.S. Pat. No. 4,090,987. The copolymeric structures disclosed were structures in which the polyether pendants in the copolymeric structures were uniformly spaced along the siloxane backbone. These structures were then of a relatively more uniform composition, but due to the nature of the siloxane condensation reaction used, were still composed of a distribution of siloxane species varying in the siloxane degree of polymerization.
Considerable reduction in the level of unreacted non-modified silicones can be achieved via a lard (preferably vacuum) distillation of the silicone lights from either the starting fluid or the copolymer product. Either method is both time consuming and costly and the latter method can jeopardize the integrity of the copolymeric product.
Thus, while a variety of products and technologies are offered in today's silicone surfactant market place which provide a broad spectrum of performance characteristics, few, if any, products are available which have a narrow uni-modal distribution and contain virtually no residual unreacted polyether nor unreacted silicone.
Excluding dimethyl oils occasionally used in HR molded systems, the conventional silicone surfactants are copolymers structurally typified by a silicone backbone (with optional branching) displaying lateral or terminal alkyl, aryl, polyether or other organic pendants. ##STR1## wherein R.sub.1 and R.sub.2 are alkyl, aryl and/or polyether.
Varying the silicone and pendant sizes, the spacing, number and type of pendant(s), the proper diluent, and other subtle structural and compositional features, produces required performance changes needed for particular applications.
Conventional, non-hydrolyzable silicone polyether compositions used in the stabilization of urethane foams are characterized by a polysiloxane backbone (with optional branching) with either terminal and/or lateral polyether pendants. In contrast however, a silicone surfactant has not been reported in the literature having a molecular "inversion" of the surfactant structure, i.e., a polyether backbone with silicone pendants. For purposes of illustration, such compositions can be depicted by the following formula: ##STR2##
Organic backbones with silane or silicone pendants have been prepared such as those having the recurring units: ##STR3## These polymers, however, contain either ester or polyethylene oxide-ketal recurring units.
Japanese workers have prepared alkoxysilane pendant polyether-polyester block copolymers having pendant silane groups attached to a polyether backbone through an oxygen atom.
In U.S. Pat. No. 4,514,315 there is disclosed a procedure for grafting ethylenically unsaturated alkylene silanes onto polyalkylene oxide polymers for use in aluminum corrosion inhibitor packages. The amount of silane monomer which was grafted onto the polyalkylene oxide polymer was up to 60 weight percent of the total product.
M. L. Wheeler in U.S. Pat. Nos. 3,418,354 and 3,573,334, disclosed and claimed olefinic silicone-organic graft copolymers which were prepared by the free radical grafting of olefinic silicones to non-crosslinked (i.e., liquid) organic polymers including polyethers. The olefinic silicones contained at least one unsaturated group, and hence the resulting graft copolymers were heavily crosslinked.
In free radical grafting, one would expect some of the unsaturated silicone compounds to react among themselves, forming polymeric compounds. Moreover, since the patentees employ silicones containing at least one unsaturated group, one would also expect grafting with silicones having more than one functionality to crosslink the polyether.
Thus, while the prior art has disclosed structures with silicone pendants from polyester and poly(ethylene oxide-ketal) backbones, and also structures with silanic pendants from polyether or poly(ether-ester) backbones, to date there has been no disclosure in the literature of discreet silicone pendant polyethers which have not been prepared by a free radical process. Hence, as indicated above, since these copolymers have polyether backbones and silicone (or silane) pendants, wherein conventional surfactants have the reverse configuration, they have been termed "inverted surfactants".
Accordingly, one or more of the following objects will be achieved by the practice of the present invention. It is an object of this invention to provide novel siloxane polyether copolymers. Another object of this invention is to provide novel silicone polyether compositions which are block copolymer compositions. A further object is to provide silicone polyether copolymers which are useful as surfactants in the manufacture of polyurethane foams. A still further object of this invention is to provide copolymers which exhibit a polyether backbone with terminal and/or lateral siloxane pendants. Another object is to provide copolymeric product mixtures which contain virtually no residual unreacted polyether nor unreacted silicone and are therefore predominantly copolymer. A further object is to provide copolymeric compositions which are composed of a narrower molecular weight distribution than conventional copolymers. A still further object is to provide copolymeric compositions which are effective stabilizers, particularly for rigid polyurethane foams. Another object is to provide rigid polyurethane foams prepared using the surfactants of the present invention. Processes are also provided for the preparation of the copolymers and the foams. These and other objects will readily become apparent to those skilled in the art in the light of the teachings herein set forth.